The role of hydrogen in microbiologically influenced corrosion and stress corrosion cracking

The phenomenon known as “microbiologically influenced corrosion” (MIC), is very closely related to hydrogen embrittlement of different metallic systems, since microorganims are also a source of hydrogen, by decatalyzing the hydrogen recombination reaction at metal surface, H_ads+H_ads→H₂. On the other hand, “stress corrosion cracking”, (SCC), refers to the synergic action of a specific aggresive environment and the stress condition, which lead to the deterioration or loss of the mechanical properties of a metallic material, linked to the presence of hydrogen. This paper summarizes the role of hydrogen in both phenomena, since the environment supports and justifies the corrosion reactions, being able to change the inside crack chemical conditions, related to the bulk solution. In this way, tensile stresses in SCC, and biological activity in MIC, must be responsible for producing a distribution of embrittlement source, generally hydrogen, with a synergic effect between both phenomena. Certain “metallurgical conditions” of the material with different strength levels associated with diverse values of hydrogen solubility and diffusivity are specially susceptible to MIC and SCC. In addition to this, the principal morphologies of attack and cracking are described.     

Influence of cerium (III) ions on corrosion and hydrogen evolution of carbon steel in acid solutions

This paper intended to investigate the influence of rare earth Ce(III) ions on the corrosion behavior of carbon steel in two acid solutions (0.5 M HCl and 0.25 M H₂SO₄) in order to control the rate of hydrogen evolution in those systems. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were used for corrosion rate and electrochemical impedance evaluation. SEM was used to examine the sample surfaces immersed in acid solutions containing the optimal threshold Ce(III) concentration (0.1 mM). All results reveal that the corrosion resistance of carbon steel in HCl is superior to that in H₂SO₄ due to the higher rate of hydrogen production in the latter. A model for the corrosion process mechanism and inhibition by Ce(III) salt for carbon steel in the two tested media is proposed.     

Hydrogen generation from the reaction of Al pretreated in acidic or alkaline solution and water

Al and Al₂O₃ film react with strong acid or alkaline solution, bring the extensive corrosion. To decrease the corrosion, Al is first pretreated with a small amount of HCl, NaOH, NaAlO₂ and a mixture of NaAlO₂+Al(OH)₃ in this work. Al pretreatment allows for the rapid removal of oxide film, shortens the induction time and ensures the initial Al–H₂O reaction rate. Typically, immersion of the pretreated Al by a mixture of NaAlO₂+Al(OH)₃ into water, generates hydrogen rapidly without an induction time, and the average H₂ generation rate reaches 5.5 mL min⁻¹. As the Al–H₂O reaction proceeds, the potential changes, which is similar to hydrogen evolution of pretreated Al in water. Hydrogen generated rapidly with the consecutive addition of Al, and the initial hydrogen generation rate reaches ~37 mL min⁻¹. Therefore, Al pretreatment by a mixed alkaline solution is an effective method to accelerate hydrogen generation for the first cycle. Rapid and consecutive hydrogen generation by the Al–H₂O reaction could provide on-demand and high-purity hydrogen, meet some equipment requirements and promote the competition in renewable-energy sources.     

Experimental study and numerical simulation on the SSCC in FV520B stainless steel exposed to H2S+Cl− Environment

Constant displacement loading tests using wedge opening loading specimens were carried out in aqueous hydrogen sulfide solution containing sodium chloride to investigate the susceptibility of stress corrosion cracking (SCC) of FV520B precipitation hardening martensitic stainless steel. Results of the SCC tests indicated that the stress corrosion critical stress intensity factor (K_ISCC) dramatically decreased in the corrosion medium investigated and decreased with the increasing of H₂S concentration. Microstructures of fracture surfaces were analyzed using a scanning electron microscope (SEM) with an energy dispersive X-ray spectroscopy (EDS). The fracture surface was typical of sulfide stress corrosion fracture. In addition, large amount of intermittent arc-crack on the side surfaces around the tip of main crack formed even no main crack propagated.A sequentially coupling finite element analysis (FEA) program was utilized to simulate the stress field and calculate the diffused hydrogen concentration distribution of specimen exposed to the corrosion medium investigated. The FEA results indicated that corrosion pit affected the stress and diffusion hydrogen distribution around the corrosion pit where large stress gradients formed. Side surface cracks initiated from those corrosion pits and propagated under the synergy of stress and hydrogen. The effect of the corrosion pit on hydrostatic stress distribution was limited in superficial zone near the side surface, thus side surface cracks propagated along the hoop direction rather than along the direction of specimen thickness. Based on the morphology observation and FEA results, it can be concluded that the SCC mechanism of FV520B steel was hydrogen embrittlement mainly and combination of anodic dissolution. Simultaneously, corrosion pitting was the precondition of side surface crack formation while the stress induced hydrogen diffusion was the dominant factor.     

Influence of process parameters on enhanced hydrogen evolution from alcoholysis of sodium borohydride with a boric acid catalyst

The hydrogen evolution via alcoholysis reaction of sodium borohydride with an H₃BO₃ catalyst was carried out for the first time. In the process of methanol and NaBH₄ (NaBH₄-MR), the effects of the H₃BO₃ and NaBH₄ concentration, and temperature parameters were examined and evaluated. The hydrogen yields by the NaBH₄-MR, NaBH₄ ethanolysis (NaBH₄-ER) and NaBH₄ hydrolysis reactions (NaBH₄-HR) with 0.2 M H₃BO₃ catalyst are 99, 62, and 88% compared to the theoretical hydrogen yield, respectively. The completion times of the NaBH₄-MR using the H₃BO₃ concentrations of 0.2, 0.4, 0.5, 1 M, and saturated acid solution were about 50, 15, 10, 2 and 1 min, respectively. The hydrogen yields obtained with 50, 15, 10, 2, and 1 min for the same acid concentration values were about 100% compared to the theoretical hydrogen value. By increasing the H₃BO₃ concentration from 0.2 M to the saturated H₃BO₃ concentration, the completion time of this NaBH₄-MR process was reduced by approximately 50 times, resulting in a significant result. The activation energy (Ea) of the NaBH₄-MR with the H₃BO₃ catalyst was 57.3 kJ/mol.     

Electrochemical preparation of a novel,effective and low cast catalytic surface for hydrogen evolution reaction

The formation of platinum nucleus on the freshly polished aluminum (Al) and anodized aluminum electrodes (Al₂O₃/Al) was studied by cyclic voltammetry. Results showed that the deposition of platinum on freshly polished aluminum from an aqueous 0.5 M phosphate buffer solution containing H₂PtCl₆ takes place rapidly through the electroreduction of dissolved Pt (IV) ions. At shorter deposition times, small particles of platinum crystals were formed on the aluminum and the surface coverage was imperfect. At longer deposition times, the size of the platinum crystals increases while their number decreases due to the coalescence and agglomeration processes. The electrodeposition of Pt on the Al electrode was conveniently carried out over the Al₂O₃/Al electrode. The electrochemical and catalytic activities of the Pt/Al and Pt/Al₂O₃/Al electrodes were studied in 0.1 M H₂SO₄ solution. In cyclic voltammetry, the two pair symmetric peaks appeared in 0.1 M H₂SO₄ solution which was attributed to the formation of strongly (H_s) and weakly bounded hydrogen (H_w). The occurrence of the third anodic hydrogen peak (H_3rd) was revealed at low scan rate and in high concentration of H₂SO₄. At potentials more negative than −0.3 V vs. SCE, the current is mainly due to hydrogen evolution reaction. The influence of the various parameters such as deposition method and amount of platinum, sulfuric acid concentration and medium temperature on the hydrogen evolution reaction is described. Finally the kinetic of the hydrogen evolution reaction is also discussed on the Pt/Al electrode.     

Using a pulsed electric current to reduce the susceptibility of high-strength steel to the stress corrosion cracking caused by hydrogen

Under the tensile loading, the damage of metals in the corrosive medium is the most destructive and harmful. In this study, the stress corrosion cracking behavior of H-charged high-strength steel in 3.5 wt% NaCl solution after electropulsing treatment was investigated. The experimental results from elongation, yield strength, fracture morphology, and polarization curves all demonstrate the positive effect of the pulsed processing, as it reduced the susceptibility of steel to stress corrosion cracking by removing hydrogen by electropulsing. The reduction in hydrogen content of the pulsed high–strength steels was attributed to electromigration and increased system free energy, which drove the hydrogen atoms in the steel to de–trap and reduced the susceptibility to stress corrosion cracking.     

Hydrogen generation by aluminum corrosion in aqueous alkaline solutions of inorganic promoters: The AlHidrox process

The research of alternative processes to obtain clean fuels has become a main issue because of the concerns related to the current energy system, both from economical and environmental points of view. Hydrogen storage and production methods are being investigated for stationary and portable applications. Up to now, a significant part of H₂ production on demand was thought to be fulfilled by using chemical hydrides, but recent studies have proved the limitations of this approach. Conversely, H₂ production based in the corrosion of light metals in water solutions is an interesting alternative. Among all of them, Al is probably the most adequate metal for energetic purposes due to its high electron density and oxidation potential. But concerning H₂ production from Al corrosion in water, a major issue remains unsolved: metal passivation due to the formation of Al(OH)₃ inhibits H₂ evolution. In this work we show the last results obtained for the generation of H₂ from water using Al powder using diverse alkaline solutions. It is confirmed that corrosion is not affected solely by the solution pH but also by the nature of the ionic species found in the aqueous medium. Moreover, we describe the AlHidrox process, which minimizes Al passivation under mild conditions by the addition of different inorganic salts as corrosion promoters, allowing 100% yields and flow rates up to 2.9 L/min per gram of Al. The feasibility of the process has been regarded in terms of stability (by conducting several successive runs) and self-initiation without an external heating.     

Hydrogen generation by aluminum corrosion in seawater promoted by suspensions of aluminum hydroxide

Nowadays, new processes of H₂ generation from water via Al corrosion are mainly limited by Al passivation. Here we report on the systematic assessment of H₂ production by corrosion of Al in seawater suspensions prepared with NaAlO₂. The reported results are encouraging, since it was observed that seawater suspensions tested can prevent Al passivation during H₂ evolution, reaching 100% yields at ca. 700 cm³ H₂ min⁻¹. XRD analysis revealed the formation of solid Al(OH)₃ (bayerite) in initial seawater suspensions. So, model suspensions were prepared using NaAlO₂ + Al(OH)₃ in distilled water, which even improved the results obtained in seawater. Suspended particles of Al(OH)₃ act as nuclei in a mechanism of seeded crystallization, which prevents Al surface passivation. Moreover, a synergistic effect of Al(OH)₃ suspensions in combination with NaAlO₂ solutions was key in promoting Al corrosion. The effect of NaCl in aqueous suspensions was also studied, but it was insignificant compared to this synergistic effect. The composition of suspensions was optimized and a 0.01 M NaAlO₂ solution with 20 g dm⁻³ Al(OH)₃ was selected as candidate to generate H₂ at pH ca. 12 with high efficiency. Consecutive runs of the selected composition were performed obtaining ca. 90% yields in all of them.     

Electrochemical investigation on the corrosion and hydrogen evolution rate of mild steel in sulphuric acid solution

Corrosion and hydrogen evolution rate of mild steel alloy have been investigated using various electrochemical techniques. Mild steel was polarized vs. saturated calomel electrode (SCE) in naturally aerated 0.1 M H₂SO₄ solution containing three newly synthesized heterocyclic compounds in different concentrations. The data obtained from polarization technique showed that the corrosion current density, i_corr, and the hydrogen evolution rate decrease with increasing concentration of heterocyclic inhibitors in 0.1 M H₂SO₄ medium, indicating a decrease in the corrosion rate of mild steel as well as an increase in the inhibition efficiency (IE) of the newly synthesized inhibitors. The impedance measurements confirmed well the polarization behaviour. Increasing the temperature leads to an increase in corrosion or hydrogen evolution rate of the mild steel and a decrease of the total resistance value (R_T) or the relative thickness (1/C_T) of the film. The obtained results were confirmed by surface examination using scanning electron microscope.     

Hydrogen storage properties of new A3B2-type TiZrNbCrFe high-entropy alloy

Crystal structure and hydrogen storage properties of a novel equiatomic TiZrNbCrFe high-entropy alloy (HEA) were studied. The selected alloy, which had a A₃B₂-type configuration (A: elements forming hydride, B: elements with low chemical affinity with hydrogen) was designed to produce a hydride with a hydrogen-to-metal atomic ratio (H/M) higher than those for the AB₂- and AB-type alloys. The phase stability of alloy was investigated through thermodynamic calculations by the CALPHAD method. The alloy after arc melting showed the dominant presence of a solid solution C14 Laves phase (98.4%) with a minor proportion of a disordered BCC phase (1.6%). Hydrogen storage properties investigated at different temperatures revealed that the alloy was able to reversibly absorb and fully desorb 1.9 wt% of hydrogen at 473 K. During the hydrogenation, the initial C14 and BCC crystal structures were fully converted into the C14 and FCC hydrides, respectively. The H/M value was 1.32 which is higher than the value of 1 reported for the AB₂- and AB-type HEAs. The present results show that good hydrogen storage capacity and reversibility at moderate temperatures can be attained in HEAs with new configurations such as A₃B₂/A₃B₂H₇.     

Influences of temperature, H2SO4 concentration and Sn content on corrosion behaviors of PbSn alloy in sulfuric acid solution

The influences of temperature, H₂SO₄ concentration and Sn content on corrosion behaviors of PbSn alloys in sulfuric acid solution were investigated by potentiodynamic curve, cyclic voltammetry (CV), linear sweeping voltage (LSV), electrochemical impedance spectra (EIS), a.c. voltammetry (ACV) and Mott-Schottky analysis. The microstructure of the corrosion layer on PbSn alloy was analyzed by scanning electron microscopy (SEM). The results showed that the corrosion resistance of PbSn alloy increased with ascending Sn content and H₂SO₄ concentration, the increment of temperature can decrease the corrosion resistance of PbSn alloy in H₂SO₄ solution. The conductivity of the anodic film on PbSn alloy was enhanced with increasing temperature, ascending Sn content and descending H₂SO₄ concentration. SEM result revealed that the corrosion film after cyclic voltammetry was consisted of tetragonal crystal, the porosity enlarged with decreasing temperature, Sn content and H₂SO₄ concentration.     

Effect of Sn and Zn alloying with Al on its electrochemical performance in an alkaline media containing CO2 for Al-air batteries application

Aluminum alloyed with other metals, such as Sn and Zn, was synthesized via fusion to trace the impact of alloying elements on the electrochemical characteristics of Al anodes. The corrosion inhibition and electrochemical tests were performed in a 5 M KOH medium in the absence and presence of CO₂ for the Al–Sn, and Al–Zn anodes and compared to the commercial aluminum. Tafel polarization exhibited that the anodic and cathodic branches display lower current densities than Al metal in pure KOH. The steady state of the open circuit voltage (E_corr.) for the studied alloys was shifted to a more negative magnitude than for Al. The corrosion current is sharply decreased, and potential is significantly shifted to less negative values in the presence of CO₂. This is due to forming of a protective layer from the carbonate of Al, Sn, and Zn on the surface. Amazing results were obtained and discussed in the case of CO₂. Electrochemical impedance spectroscopy (EIS) results exhibited that charge transfer resistance (R_ct) values rise with alloying elements. The data of Tafel plots are consistent with those of EIS. The alloying of Al with Sn and Zn elements significantly affects capacitance, hydrogen evolution process suppression, and charge-discharge efficiency. This reveals that the highest potential value in the presence of CO₂ in the charging process is obtained for Al–Zn alloy, while the most negative potential is obtained for Al in the discharging process with CO₂. Moreover, the discharge time is higher in the alloys than in commercial Al in the absence and more in the presence of CO₂. The produced alloys are thought to provide good anodes for long-life rechargeable batteries.     

Kinetics study on the generation of hydrogen from an aluminum/water system using synthesized aluminum hydroxides

Kinetics study on the generation of hydrogen from an Al/water system is performed. The reaction is affected by three major factors such as the concentration of hydroxyl ions (pH values), catalysts, and temperature. However, these factors are interacted and sometimes difficult to separate. This study demonstrates how these factors affect the generation of hydrogen in an Al/water system. Aluminum hydroxide, Al(OH)₃ (bayerite phase), synthesized using a chemical solution method, is proved to be a very effective catalyst for the reaction of Al and water. Approximately 95% yield (1300 mL) of hydrogen is produced from 1 g Al in 10 mL water using 3 g Al(OH)₃ catalyst at room temperature within 1 minute. The generation rate of hydrogen is accelerated due to the catalyst Al(OH)₃ and the exothermic heat. In this report, a ball‐mixing process, the ratio of Al:Al(OH)₃:H₂O, and the reacting temperatures are investigated to clarify the effect of catalyst Al(OH)₃. The synthesized Al(OH)₃ catalyst is found to reduce the activation energy of Al/water reaction from 158 kJ/mol to 73.3~76.9 kJ/mol. The roles of hydroxyl ions (ie, pH values), temperature, and catalyst on this phenomenal reaction are explained using a kinetics study and the concept of Fick first law. The 3 factors all improve the flux of hydroxyl ions through the passive Al₂O₃ layer; therefore, the generation of hydrogen is enhanced.     

Enhancement of ammonia synthesis activity on La2O3-supported Ru catalyst by addition of ceria

The addition of Ce species in La₂O₃ can enhance the number of defect sites and generate the Ce_1-xLa_xO_2-δ solid solution, thereby increasing the amount of the exposed ruthenium species and proportion of metallic ruthenium species. The presence of Ce species in Ru/La₂O₃ promotes the desorption of hydrogen, and hydrogen species prefers to desorb in the H₂ molecule formation pathway. On the other hand, the difference in the Ce addition method strongly affects the exchange between the adsorbed hydrogen species on Ru catalyst with the gaseous hydrogen species. Owing to improvement of the proportion of oxygen vacancy, Ru⁰ and number of the exposure of ruthenium species, H₂ species adsorbed on Ru/LaCe–C prepared by coprecipitation method preferentially desorbs in the formation of H₂ pathway, and a large proportion of the adsorbed H species would exchange with the hydrogen species from the gaseous phase, which leads to improvement of ammonia synthesis rate by 75% in comparison with Ru/La₂O₃ catalyst.     

VC3H3 organometallic compound: A possible hydrogen storage material

This work reports the hydrogen uptake capacity of V-capped and V-inserted VC₃H₃ organometallic complexes using density functional theory (DFT) with different exchange and correlation functionals. Maximum of five and three H₂ molecules are adsorbed on V-capped and V-inserted VC₃H₃ structures, respectively. This corresponds to the hydrogen uptake capacity of 10.07 and 6.66 wt% for the former and the latter, respectively. The first added hydrogen molecule is adsorbed in dihydride form on V-capped as well as V-inserted VC₃H₃ complex. A complex with a dissociated hydrogen molecule adsorbed has higher binding energy than that of molecular hydrogen adsorbed. The nature of interactions between H₂ molecules and organometallic complex is studied using many-body analysis approach. Thermo-chemistry calculations are performed to see whether H₂ adsorption on V-capped complex is energetically favorable or not for room temperature hydrogen storage.     

Synergistic effect of the fresh Co,Ni, and anion ions on aluminum or magnesium with water reactions

To analyze the effect of Co and Ni on hydrogen generation in water, the reactions of Mg and Al with water in CoCl₂ and NiCl₂ solutions are studied in terms of amount of H₂ produced and rate of reaction. Mg rapidly reacts with water in CoCl₂ and NiCl₂, producing high amount of H₂ without induction time. While there is a short induction time is detected for Al─H₂O reaction in CoCl₂ and NiCl₂. In addition to the galvanic cell behavior of the Mg (Al)/Co (Ni) compounds formed, Co and Ni catalyze the hydrogen production reaction; however, the agglomeration of Co or Ni leads to a noticeable decrease in H₂ production. The open‐circuit potential in CoCl₂ and NiCl₂ solutions after the addition of Mg or Al at ambient temperature shows an obvious change, coinciding with the initiation of the hydrogen generation process. Mg rapidly reacts with water in Co (Ac)₂, CoSO₄, Ni (Ac)₂ and NiSO₄ solutions as a consequence of its intrinsic metallic properties and of the formation of Co or Ni. The hydrogen production amount is lower (<200 ml g^?1) in Co (NO₃)₂ and Ni (NO₃)₂, even after adding NaCl. No reaction occurs when adding Al in CoSO₄, Co (Ac)₂, Co (NO₃)₂, NiSO₄, Ni (Ac)₂, and Ni (NO₃)₂. The synergistic effect of Co, Ni, and anion ions in water affects the rate of Al or Mg corrosion and hydrogen generation.     

Phase change performance assessment of salt mixtures for thermal energy storage material

The phase transition performance of the CaCl₂ · 6H₂O–Ca(NO₃)₂ · 4H₂O composite salt system with nucleating and thickening agents was investigated in this paper. The CaCl₂ · 6H₂O–Ca(NO₃)₂ · 4H₂O composite salt system was prepared by adding Ca(NO₃)₂ · 4H₂O (12 wt%) to CaCl₂ · 6H₂O. Different nucleating agents including SrCl₂ · 6H₂O, SrCO₃, BaCl₂, BaCO₃, Na₂B₄O₇ · 10H₂O, H₃BO₃ and NH₄Cl were used to address the problems of phase segregation and supercooling phenomena during the phase change process. The results show that the single nucleating agent SrCl₂ · 6H₂O or the mixture of nucleating agents with 2 wt% SrCl₂ · 6H₂O, 1 wt% BaCl₂ and 0.5 wt% of thickening agent carboxyl methyl cellulose is the most suitable for this system. The latent heat remained constant at about 116 J/g before and after adding the agents. Density functional theory was used to further investigate the microstructure‐related reason for the salt–water separation and supercooling phenomena. It can be deduced that the hydrogen bond is the vital factor involved during the phase transition. The aim of adding thickener was to form more hydrogen bonds which encapsulated the hydrated species and made it difficult to lose the hydrated waters. The main purpose of adding nucleating agent was to break the metastable state among microscopic species. The results of this work indicate that the CaCl₂ · 6H₂O–Ca(NO₃)₂ · 4H₂O salt mixture has potential as a thermal energy storage material. Copyright © 2017 John Wiley & Sons, Ltd.     

Hydrolytic reaction of waste aluminum foils for high efficiency of hydrogen generation

Hydrolyzed waste aluminum foil in low alkaline aqueous solution and concomitant additives are evaluated to generate hydrogen gas. The result of hydrogen generation using wasted Al foil is efficient in comparison with traditional Al powder. A polythene film coated on waste Al foil was removed by immersing into nitric acid for 5 h prior to hydrolyzed reaction. Low alkaline solution (0.75 M NaOH) combined with Bi additives at elevating temperature (70 °C) in waste Al foil-water hydrolysis system enable to increase hydrogen generation rate to 30 ml s^?1 g^?1 and total volume 1300 ml g^?1. The optimized result is attributed to the micro-galvanic cell formation between Al/Bi and removing hydroxide on Al foil surface by alkaline solution. In this report we develop low cost and waste recovery by hydrolyzing waste Al foil. High efficiency of hydrogen generation is achieved by low alkaline concentration and reducing activation energy. Al oxidation mechanism is explained by the linear-parabolic growth model and polarization curves indicate that corrosion potential of Al foils did not abruptly degrade and the corrosion capability with reliability were verified.     

Hydrogen generation by splitting water with Al–Li alloys

In order to prevent the inert alumina film from forming on the surface of Al metal particles, Li is added into Al to form Al–Li alloy. It can improve the reactivity of Al with water. The prepared Al–Li alloy can rapidly split water to produce hydrogen. With increasing Li content of alloy, the hydrogen generation rate is promoted. The ultimate hydrogen yields of samples can reach 100%. The effect of initial water temperature on the hydrogen generation has been investigated. Even in the water at 0 °C, hydrogen can also be produced rapidly. Composition of solution has some effect on the hydrogen generation. Especially, Mg²⁺ or NO₃^? has negative influence on the hydrogen generation and can reduce the ultimate hydrogen yield of alloy. Longer air exposure time will also decrease the ultimate hydrogen yield. After reaction, Al and Li enter into the residue in the form of LiAl₂(OH)₇·2H₂O and LiAl₂(OH)₇·xH₂O or Al(OH)₃. After calcinations, these reaction by‐products can be easily recycled by existing metallurgical process. Copyright © 2012 John Wiley & Sons, Ltd.